High RPM misfire
Discussion
Now that I'm getting more confident I'm venturing into the top of the revv range now and then.
However at around 5,000rpm it's like I'm hitting the revv limiter.
I've seen it pull right round to the 6k mark before so I'm quite sure it's not the revv counter being in-accurate.
I cleaned the cap and rotor today and checked all the leads are secured. I read that swapping the relays around can cure this?? I also read that the fuel pump could be to blame but that it is rare for this to be the issue?
I also know it does it at any load - not just under load, it will do it just by revving on the spot
However at around 5,000rpm it's like I'm hitting the revv limiter.
I've seen it pull right round to the 6k mark before so I'm quite sure it's not the revv counter being in-accurate.
I cleaned the cap and rotor today and checked all the leads are secured. I read that swapping the relays around can cure this?? I also read that the fuel pump could be to blame but that it is rare for this to be the issue?
I also know it does it at any load - not just under load, it will do it just by revving on the spot
It could be the coil if it does it in any load, as the coil voltage drops quite sharply (even on a good one) as the rpm rises due to the lack of dwell or recharge time for the coil on a V8 engine, so it the coils poor to start with, the spark could simply be failing at higher RPM. Any half decent old school garage should be able to do an HT check for you. I would not expect fuel or ECU at this point as you dont need much fuel when rev'ing it in neutral.
Had exactly your problem, was checking it over in the garage and noticed the manifolds glowing too 
Visual check of HT leads seemed ok and all appeared to be snugly fitted to the plugs so I was getting worried about an expensive failure. Had a doubly thorough check of the leads and number 8 had a hairline fracture in it where it goes in to the shroud at the end. Quick trip to my mates motor factors, £25 and a new set of Bosch leads and she pulls strong all the way round to the proper rev limiter now.
Seems at low revs/pootling around the lead was ok, but when being asked to work hard it couldn't cope.
Hope your fix is as simple
Visual check of HT leads seemed ok and all appeared to be snugly fitted to the plugs so I was getting worried about an expensive failure. Had a doubly thorough check of the leads and number 8 had a hairline fracture in it where it goes in to the shroud at the end. Quick trip to my mates motor factors, £25 and a new set of Bosch leads and she pulls strong all the way round to the proper rev limiter now.
Seems at low revs/pootling around the lead was ok, but when being asked to work hard it couldn't cope.
Hope your fix is as simple
Yes thanks I do as well.
So we've got miniman saying his was the intake, yours the HT lead and also in the bible Steve Heath's Griff had a 5k + psuedo revv limiter issue and his was (Amongst other things) the coil.
Funny that for how different these 'faults' are they all manifested themselves as not revving properly past 5,000rpm.
Thanks again for your comments guys. A new coil is never a bad idea so I think I will start there. The TVR center fitted new leads for me in October (not saying they won't be possibly faulty though)
So we've got miniman saying his was the intake, yours the HT lead and also in the bible Steve Heath's Griff had a 5k + psuedo revv limiter issue and his was (Amongst other things) the coil.
Funny that for how different these 'faults' are they all manifested themselves as not revving properly past 5,000rpm.
Thanks again for your comments guys. A new coil is never a bad idea so I think I will start there. The TVR center fitted new leads for me in October (not saying they won't be possibly faulty though)
I had this on my 500. Pulled like a train and then suddenly dropped off like a rev limiter. This was shown also on a rolling road day and you could see the lambda value suddenly lean right off - very odd.
Just by luck shortly after, I was working under the back end of the car and noticed the fuel filter bracket was sat at an angle and had kinked the fuel pipe. It was not getting quite enough juice at higher revs. Pipe straightened, then problem disappeared!! Cost of repair £0 - Happy days....
Just by luck shortly after, I was working under the back end of the car and noticed the fuel filter bracket was sat at an angle and had kinked the fuel pipe. It was not getting quite enough juice at higher revs. Pipe straightened, then problem disappeared!! Cost of repair £0 - Happy days....
Cool. We'll a new coil turned up today which is always good so when fitting that I will have a see at all the fuel lines. Has recently had a fuel filter from The TVR Center so I'd imagine they put it back right. Couldn't have broken either, well it did this long before I had the filter changed.
Its all good though, all these 5k misfire easy fix stories!
Its all good though, all these 5k misfire easy fix stories!
Bitzracing, thank you for your suggestion, the new coil fixed it!
Also another niggle that turned up towards the end of last year disappeared - the rev counter needle started to bob around very slightly at about 2,000rpm - 3,000rpm and that has now stopped. Nice because I was sure it didn't always do that! Thought my rose tinted spectacles might have been playing mind games with me!
Also another niggle that turned up towards the end of last year disappeared - the rev counter needle started to bob around very slightly at about 2,000rpm - 3,000rpm and that has now stopped. Nice because I was sure it didn't always do that! Thought my rose tinted spectacles might have been playing mind games with me!
Edited by dog man on Thursday 3rd March 17:24
Damn! Its still there! Why did I think it was cured? Well, on the day I fitted the new coil I gave it one blast in 1st gear and it revved cleanly to 6k. I had driven 5 miles on the M1 to let it warm up then on the way back I gave the loud pedal a good prod so maybe it's temp related? Today I had been running around a fair bit before I noticed it's still there - the engine/underbonnet would have been well warm by then.
Tbh I dont like caning it so hadn't noticed til this afternoon that in fact it still isn't cured! Oh well back to the drawing board, oh but at least the coil cured the revv counter!
Cock!
Tbh I dont like caning it so hadn't noticed til this afternoon that in fact it still isn't cured! Oh well back to the drawing board, oh but at least the coil cured the revv counter!
Cock!
Yep, check.
Think I might have something now.
I'd just gone over the connectors to the ignition module and AFM and suddenly the car wouldn't start..
However, quick look back under the hood and when I'd reconnected the ignition module plug the yellow wire had simply fallen off! Right where the wire is crimped into the connector.
It must have been hanging on by a thread for ages now.
Annoyingly there wasn't a very elegant way of repairing this without soldering it and far too much of the wiring would need to come out to remove that part of the wiring harness. So I had to split the plug open, shove the unbroken connector back on the module and attach the broken wire via a crocodile clip and it started again.
So lets hope when I buy a new plug (ford) and attach it all properly the misfire has gone. Certainly it wouldn't have transmitted the proper current with only a strand or two of wire so it can only help.
Think I might have something now.
I'd just gone over the connectors to the ignition module and AFM and suddenly the car wouldn't start..
However, quick look back under the hood and when I'd reconnected the ignition module plug the yellow wire had simply fallen off! Right where the wire is crimped into the connector.
It must have been hanging on by a thread for ages now.
Annoyingly there wasn't a very elegant way of repairing this without soldering it and far too much of the wiring would need to come out to remove that part of the wiring harness. So I had to split the plug open, shove the unbroken connector back on the module and attach the broken wire via a crocodile clip and it started again.
So lets hope when I buy a new plug (ford) and attach it all properly the misfire has gone. Certainly it wouldn't have transmitted the proper current with only a strand or two of wire so it can only help.
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